A low testosterone level should always be confirmed by repeat testing, preferably before 11 AM, before eating. Testing should not be conducted during an acute illness. Although total testosterone is the most common screening test, some men may also require measurement of free testosterone levels.

Deficiency of testosterone may be very common among adult men in the United States.

Those at particular risk include men with Type 2 Diabetes (estimated prevalence of 30-50%!), obese men, and men over the age of 70-75 years-old.

The HIM study (Hypogonadism in Men) provides one estimation of testosterone deficiency in otherwise healthy men.

The study found that 38.7% of men 45 years or older evaluated during well patient primary care visits had testosterone levels of less than 300 ng/ml. Most of these men did not know their testosterone levels were depressed.

Male testosterone production occurs in the testicles. Production is controlled by lutenizing hormone (LH), a hormone made in the pituitary gland.

Low testosterone levels may result from disease in the testicles (primary hypogonadism) or disease in the hypothalamus and pituitary (secondary hypogonadism).

Some men have abnormalities at multiple levels.

Identification of the cause of testosterone deficiency requires further blood testing.

Radiologic imaging of the pituitary is recommended if secondary hypogonadism is suspected.

Whatever the cause, adult onset low testosterone may be associated with complaints of fatigue, reduced interest in sex, less frequent spontaneous erections, and loss of muscle strength.

Since the symptoms are nonspecific, diagnosis of testosterone deficiency requires a high degree of clinical suspicion. Symptoms typically increase as testosterone levels decline.

Replacement of testosterone via gels, patches or injections will often result in resolution of symptoms with improved energy and sexual function.

Once testosterone therapy is initiated, it is important to monitor testosterone levels as up to 30% of men will require a dose adjustment.

Since testosterone therapy may result in side effects such as increased number of red blood cells and acne, close medical follow-up is very important.

Other potential side effects include infertility, swelling of the legs and breast enlargement.

Although a careful prostate evaluation must be conducted before beginning therapy, evidence doesn't support an increased risk of prostate cancer.

Several studies published in 2013and 2014 suggested that testosterone therapy may raise the risk of heart-related events.

Although the studies were plagued by a variety of methodological errors, and contradict prior reports, caution is recommended in the setting of active heart disease. Comments regarding the studies were published in the March 5, 2014 issue of JAMA.

Randomized trials were recommended to further elucidate this potential risk.

As of 2016, most evidence from existing studies doesn't support an increased risk of cardiovascular events.

If left untreated, testosterone deficiency may cause thinning of the bone (osteopenia).

It is unknown if testosterone-induced bone thinning is associated with an increased fracture risk.

The evaluation and treatment of testosterone deficiency should be discussed with your physician, and never initiated or continued without regular medical follow-up.